Electro-osmosis driver unit combined with electrolytic detector for taking derivatives



R. M. HURD ET AL ER UNIT COMBINED WITH ELECTRO DETECTOR FOR TAKINGDERIVATIVES Filed NOV. 50, 1955 G. T. KEMP ATTOR EYS O O Q O Q O UnitedSttes atet ELECTRO-OSMOSIS DRIVER UNET QOMBENED WITH ELECTRLYTICDETECTOR FR TAKING DERIVATIVES Ray M. Hurd, Austin, and George T. Kemp,Paint Rock, Tex., assignors, by mesne assignments, to the United Statesof America as represented by the Secretary of the Navy Filed Nov. 30,1955, Ser. No. 550,230 9 Claims. (Cl. 310-2) This invention relates to adevice for taking the time derivative of a small electrical current byelectrolytic means. More specifically, the invention relates to the newand novel combination of an electro-osmosis driver unit and anelectrolytic detector of linear characteristics for taking the timederivative of an electrical current by electrolytic and hydraulic means.

The system of the instant invention is somewhat analogous to anelectrical circuit including a fluctuating voltage source of directcurrent potential and a circuit therefor including a series resistanceand a series capacitance wherein all elements are of the linear type.The analogous current charging the analogous capacitor is ran imperfecttime derivative of the analogous potential.

In a device of the instant invention a linear relationship is `obtainedbetween the voltage applied to the electro-osmotic cell and the pressureof the fluid therein. By combining an electro-osmotic cell and a linearelectrolytic detector of the character herein to be described, an outputcurrent relationship is obtained in an overall combination of thesedevices which is a linear relation with respect to the fluid velocity orthe volumetric flow of fluid in the system until an equilibriumcondition is approached.

The electro-.osmotic cell of the instant invention is of a characterincorporating a housing having a fritted lter glass partition disposedtransversely of the central portion thereof to provide a pair ofenclosed volumes which are in fluid communication through the pluralityof capillaries of the fritted glass or other suitable porous ceramicdisc. The device is provided with a pair of electrodes in closeadjacency with the filter disc and terminating in external connectionsacross which the direct current input potential is applied. It is wellknown in the art that when a potential is applied across the plates orelectrodes of an electro-osmotic cell there occurs a flow of thecontained liquid. This liquid may be distilled water or any other fluidsuitable for the purpose such for example as acetone or acetonitrile.This fluid flow effects a distending of one of the pair of flexiblediaphragms which constitute the outer walls of the contained volume. Thepolarity of the applied potential determines the direction of fluidllow.

The electro-osmotic cell construction comprises a pair of diaphragms ofsuitable resilience disposed across the opposite ends of the cell in amanner to enclose both of said volumes in the housing. Theelectro-osmotic device is well adapted for coupling at one of thediaphragms to drive directly a linear electrolytic detector.

The linear detector may also be assembled as a complete assembly andarranged in spaced relation with respect to the electro-osmotic driverin which case the final assembly of the two cell units is made bysimultaneously immersing the two cell units and fixing the jointunderwater in a manner whereby the intervening space between Ithe twocell assemblies is completely filled with water. This provides anadditional closed volume which as aforesaid is completely filled with aliquid such as distilled water to provide a lluid driving arrangementfor the diaphragm of the detector cell from the diaphragm of theelectro-osmotic cell. The linear detector to which the electro-osmoticcell is coupled comprises at least one substantially rigid diaphragm anda flexible diaphragm in a spaced arrangement to enclose a volume offluid therebetween.

Disposed in the casing of the detector cell which functions inconjunction with the two diaphragms of this cell to provide `a closedvolume is a dividing wall or partition substantially separating thedevice into a pair of fluid chambers in which is contained a solution ofiodine iodide, or other applicable oxidation reduction system of ions.Suitable electrodes are provided in the respective chambers and anelectrical bias source arrangement connected therebetween to provide forthe concentration of l2 molecules of the solution in one chamber and adilute iodine solution in the the second chamber, there being a meansproviding fluid and electrolytic communication between the chambersdisposed in the intervening wall portion. The wall portion additionallyincludes a cathode assembly which has a negative polarity with respectto an anode in the chamber driven by the electro-osmotic cell, whereby aflow of electrolyte from the first chamber to the second chamberproduces a current and voltage in the external circuit as willhereinafter become apparent.

The arrangement of the system is such that the output current as derivedfrom the ytwo cell combination is a derivative with respect to time ofthe voltage of the direct current signal applied to the electro-osmoticdriver cell.

It is an object of the instant invention -to provide an apparatus fortaking the time derivative of a small electric current and providing anoutput therefrom which is proportional to the derivative of the voltagewith respect to time.

In conjunction with the foregoing object, it is a further object toobtain an approximate or imperfect derivative by a device of thecharacter to be heinafter described and with a low consumption ofelectrical power.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. l is a generally diagrammatic view in vertical section of acombined electro-osmotic driver and linear detector cell of the instantinvention;

FIG. 2 is a graphical illustration showing curves com paring themagnitude of output current and time constant of a typical combinationof an electro-osmotic cell and linear detector cell for various rates ofincrease of an applied signal;

FIG. 3 is a curve of generally similar characteristics to that of FIG. 2and as obtained by a device of a design of the instant invention foroperation under different input current characteristics.

Referring now to the drawings and more particularly to FIG. 1 thereof,the combined electro-osmotic driver cell and linear detector cell inaccordance with a physical embodiment of the instant invention isindicated generally by reference character 1. The overall systemcomprises an electro-osmotic device assembly 10 and the linearelectrolytic detector 11 the casing `of each of which is composed of aplastic material suitable for the purpose such for example aspolymonochlorotrilluoroethylene and which as manufactured by the W.Kellog Company of Newark, New Jersey, is known in the trade andhereinafter referred to as Kel-F. This plastic possesses desirablecharacteristics for this type of application in that it is substantiallyinert to corrosion by the liquids used for filling the containers andmore particularly does not leach out impurities of a detrimentalcontaminating character to the iodine solution used in the lineardetector.

aoeasee The linear detectorcell unit 1:1 provides `for a closed housing13 of Kel-F for the electrolyte fluid contained therein while theelectro-osmotic driver unit is provided with a casing 12 for containingacetone or water.

In a physical embodiment of the device the general structure of which isshown diagrammatically in FIG. l, the casings =12 and 13 are eachprovided with a pair of flanges or end ring members preferably of -brassand l0- cated at 15 and 16; the members 16 being disposed to retain theouter diaphragms 19 and 21 for the respective cells while the otherflanges 15 are disposed in abutting engagement with respect to eachother to retain the inner closure diaphragms 19 and 20 of the two cellsand contain the intermediate fluid at 4. The respective pairs of flanges15 and 16 are clamped as by a plurality of through bolts 14 or othersuitable clamping means prior to the assembly of the two cell units.They are mutually sealed by a neoprene rubber O ring 17 after assemblyof the individual cell units. The members 15 are secured and maintainedin sealing engagement with the 0 ring 17 by a plurality of bolts 18 orother suitable sealing arrangements as desired.

The electro-osmotic cell casing 1-1 is closed by a pair of flexiblenormally bulged diaphragms 19 and 19 composed of any suitable plasticsuch for example as a vinylite. The casing 12 is further provided with acentrally disposed integral partition portion 22 extending across theinterior of the cell to divide the same generally into a pair ofchambers 2 and 3. A centrally disposed opening or orifice for iiuidcommunication between the chambers is provided at 23 and is arranged toreceive and seat a fritted glass disc 24, or other porous ceramic or thelike, of a character providing a substantially uniform pattern ofcapillary orifices therethrough by which fluid can move from chamber 2to chamber 3 when the cell -is activated. This disc is retained by athreaded annular plug or retaining ring 25 of Kel-F plastic. Disposed onopposite surfaces of the fritted disc and in the circuit provided byleads 26 and 27 are a pair of identical depolarizing electrodes 28 and29, as, for example, silversilver chloride, A'g/AgCl. The electrodes 28and 29 are connected to a source of current indicated generally at EU)and applied to the lead terminals 30 and 31. The electrodes 28 and 29may be supported in adjacency to the glass disc in any suitable mannernot shown. If desired, the electrodes 28 and 29 may be of the samediameter as the disc and fitted close to the disc on both sides; theleads 26 and 27 being taken out through the sides of the casing body 12.It is to be understood that the electrodes are also porous masses or ofperforated sheet material and permit a substantially free flow of liquidtherethrough. A certain amount of hydraulic resistance is necessarilypresent in this construction of the cell 10. This resistance to fluidflow is presented by the electrodes and the capillaries of the glassdisc, and this lumped resistance functions in a manner as generally tobe described.

The linear detector body 13 is likewise of Kel-F plastic and providedwith a wall 32 for dividing the cell into two chambers 5 and 6. The wall32 is provided with an opening therethrough at 33. A Kel-F plasticbutton cathode 34 is sealed into the opening in the center of the wall33. It is provided with a small orifice 35 and the lead 36 can thereforebe taken out through this partition to the outside of the casing.` Oneconstruction of the cathode consists of a plastic plate 37 of 0.0005"thickness with an 0.0115 diameter hole 35 through the center. This holeis backed up by approximately l0 pieces of 150 mesh platinum gauzegenerally indicated at 38 and held in place by sealing in the Kel-Fannular ring 37.

Disposed in the chamber 5 of the detector unit is an anode 40, while thechamber 6 is provided with a separating cathode 41. This chamber -isfilled with an electrolyte solution of iodine and is located between thestiff diaphragm 20 and the partition wall 32.. 'I'his is a platinumelectrode which is connected to an external circuit in a manner to beprovided a positive bias by the battery indicated at 42. This batteryadvantageously provides a potential of approximately 0.9 volt. A secondelectrode 41 hereinafter designated as the separating cathode isdisposed in the chamber 6 provided between the opposite face of thepartition wall 32 and the outer exible bulged diaphragm 21. Thisseparating cathode 41 along with the main cathode at 38 are of negativepolarity with respect to the anode 40. The derivative output of thecircuit appears across the terminals 45 and 46 of leads 43 and 44 and asshown is connected through a microarnmeter `for the measurement of thecurrent ow. This microamrneter provides continuity of the circuit fromthe anode to the cathode and provides a load resistance across which aderivative voltage signal may be obtained and by means of which thecurrent flow may be measured.

Prior to the operation of the detector unit 11, which is biased at avoltage of 0.9 volt with electrodes 38 and 41 negative with respect toelectrode 40, the cell is allowed to stand for approximately 2 daysduring which time iodine molecules will be transferred electrochemically`from the output side of the detector containing electrode 41 to theinput side containing electrode 40. The electrolyte solution in theseparating cathode side chamber I6 will then be very dilute in iodinewhile that in the anode chamber side 5 will be quite concentrated.Thereafter when the device is placed in operation its function is suchthat fluid in the electro-osmostic cell flows in a direction toward thenegative osmostic electrode 29 when a voltage is impressed across theelectrodes 28 and 29. Referring now to FIGS. 2 and 3, thiselectrolytically produced hydraulic pressure is proportional to thevoltage applied to the cell. The resultant flow of fluid in the combinedsystem is restricted by the total acoustical resistance hereinafterreferred to as (Ra), of the fritted glass disc 24 and the detectorcathode elements 35 and 38. The flow acting through this acousticresistance functions to effectively charge the acoustical capacitance asprovided by the diaphragm systems of the two combined cells and willeventually charge this series condenser arrangement to fully distenddiaphragm 20, and will eventually stop the flow for any constantimpressed voltage. The current I picked up in the electrode circuit of40 and 38 is linear with the ow of the electrolyte solution through thecathode orifice 35 provided the ow is from the concentrated side to thediluted side, i.e. chambers 5 to 6, except that there is a smallbackground current present under no flow conditions. The output currentderived therefrom is the time derivative of the voltage E(t) impressedacross the electro-osmotic cell electrodes, with a time constant RCa ofthe acoustic system.

After a voltage has been impressed across the electroosmotic cell andthe fluid allowed to flow, there is an increasing pressure producedacross the condenser. When the voltage is reduced or removed from theosmotic cell, pressure across the condenser forces the fluid to ow inthe opposite direction until the pressure drop is relieved. The detectorcurrent does not increase above background When this back-flow occurssince a dilute electrolyte solution is flowing through the cathodeorifice 35. It is to be understood that the unit may be operated in sucha way that a positive Voltage of the electro-osmotic cell may produce aflow of dilute solution through the cathode orifice 35 and when thevoltage is reduced the backow will produce a detector current across theanode, main cathode circuit of the linear detector cell and produce adetector current proportional to this ow.

It is to be understood that the fritted disc may be held in place byheat sealing it to the plastic and that the cell bodies can be ofavmachined or molded configuration. The seals may be obtained by heatingafter the filling of the space between the diaphragms 19' and 20 of theelectro-osmotic cell and the detector cell has been completed. If heatsealing is used to rit these two cell units together the O ring 17 maybe omitted.

Obviously many modiiications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. Ina derivative cell device of the character described, thecombination of an electro-osmotic driving cell for producing a iluidliow in response to an input current applied thereto, and a linearelectrolytic detecting cell coupled to said electro-osmotic cell toprovide an output signal proportional to the first derivative withrespect to time of said input current.

2. An electro-acoustic system fottaking the time derivative of smallelectrical currents, comprising a circuit having an electro-osmoticdriving cell connected `for application of an input current thereto forproviding hydraulic fluid ilow therein, and a linear electrolyticdetector cell coupled to said first named cell for providing anelectrical output signal proportional to the time derivative of saidinput current in response to fluid flow therein as produced by hydraulicfluid flow in said electro-osmotic cell.

3. A hydro-acoustic derivative taking analogic circuit of a characteranalagous to a iluctuating DC. potential source connected to charge aseries capacitance through a series resistance, which comprises a sourceof signal current potential, an electro-osmotic driver cell, and anhydraulically driven electrolytic linear detector cell acousticallycoupled thereto and of a character for providing an output proportionalto the time derivative of said input signal current.

4. The combination of an electro-osmotic driver cell, a linear detectorcell, and means for providing hydroacoustic coupling between said cellswhereby an output voltage proportional to the iirst time derivative of asignal voltage applied to said electro-osmotic cell may be obtained atthe output of the linear detector cell.

5. In combination, an electro-osmotic cell, and means hydro-acousticallycoupled thereto for deriving an output signal proportional to the timederivative of an input sig` nal applied to said electro-osmotic cell,said means cornprising a closed cell filled with an electrolyticsolution, a plurality of electrodes comprising an anode and at least twocathodes disposed in said closed cell in contact with said solution, anelectrical circuit including a source of bias potential connectedbetween said anode and one of said cathodes, and a circuit for obtaininga linear output with electrolyte flow between said anode and a secondone of said plurality of cathodes.

6. An apparatus of the character described comprising an electro-osmoticcell enclosed by a pair of diaphragms, a pair of depolarizing electrodesdisposed therein, an electrolytic linear detector cell enclosed by asecond pair of diaphragms, mutual coupling means disposed between theadjacent diaphragms of said cells, and detector electrodes comprising ananode and an oriiice type detector cathode in said electrolytic detectorcell, so disposed and connected -as to provide an output signalproportional to the first time derivative of the applied input currentilowing in the circuit of said depolarizing electrodes.

7. The apparatus of claim 6 further characterized by the inclusion of aseparating cathode in said detector cell in addition to the detectinganode and cathode therein, a source of biasing potential connectedbetween said anode and said separating cathode for providing an initialdifferential in ion concentration in the cell and on opposite sides ofsaid detecting cathode, and a partition member carrying said detectorcathode for dividing said electrolytic cell into a pair of chamberswhich are of diiering electrolytic concentrations after an initial ionseparation as eiected by said biasing source.

8. In combination in a hydro-acoustic derivative circuit, anelectro-osmotic cell, a linear electrolytic detector cell, and lmutualcoupling means disposed therebetween in a manner whereby saidelectro-osmotic cell functions to hydraulically drive said detector cellunder electrical input energization applied thereto, said detector cellhaving a system of electrodes connected to provide an output voltageproportional to the first derivative of the voltage applied to saidelectro-osmotic cell with hydro-acoustic coupled driving energizationthereof.

9. The combination of an electro-osmotic driver cell adapted forenergization from an electrical power source external thereto and alinear electrolytic detector cell, said cells being mutuallyhydraulically inter-connected, and means for obtaining therefrom anoutput voltage from the detector cell which is proportional to the lirstderivative of the energization voltage for said driver cell.

Hardway Dec. l, 1953 Root m, July 27, 1954

1. IN A DERIVATIVE CELL DEVICE OF THE CHARACTER DESCRIBED, THECOMBINATION OF AN ELECTRO-OSMOTIC DRIVING CELL FOR PRODUCING A FLUIDFLOW IN RESPONSE TO AN INPUT CURRENT APPLIED THERETO, AND A LINEARELECTROLYTIC DETECTING CELL COUPLED TO SAID ELECTRO-OSMOTIC CELL TOPROVIDE AN OUTPUT